Many types of digital-to-analog converter (DAC) circuits include a resistor network having individual resistors connected by a switch network to either a reference voltage or ground as a function of individual bits of a digital input. An analog output voltage produced on a node of the resistor network typically represents a conversion of the digital input to the analog domain.
Certain problems arise with the use of such resistor and switch networks in DAC circuits, however. Connections of the resistor network by the switch network to the reference voltage or ground depend on the value of the digital input at any given time, and therefore conductor lines supplying the reference voltage and ground experience a variable current draw. Additionally, the resistor and switch networks typically include a relatively large number of resistors and switches connected to these conductor lines, with these connections distributed over a physical dimension of the conductor line, resulting in parasitic resistances existing in the conductor line between the connections. The variable current draw then combines with the distributed parasitic resistances of the conductor lines to produce voltage levels delivered to the individual switches and resistors of the switch and resistor networks that vary from intended reference voltage or ground voltage values as a function of the digital input, which degrades the linearity of the DAC circuit.
Therefore, a need exists for DAC circuits having switch and resistor networks connected to one or more reference or ground voltages as a function of a digital input, but which show improved linearity in the presence of distributed parasitic resistances of conductor lines supplying these reference or ground voltages.